Method of batch cementing



Fwaoii OR 292939904 Aug. 25, 1942. KAlL 2,293,904

' METHOD OF BATCH'CEMENTING Filed Sept. 22, 1959 /5 g4; Fig i V RAYP131625.

w .ifiimu BY bfom (ll-W ATTORNEYJ,

WELLS? Patented Aug. 25, 1942 METHOD OF BATCH CEMENTING Ray S. Kail,Houston, Tex, assignor to Baker Oil Tools, Inc., Vernon, Calif., acorporation of California Application September 22, 1939, Serial No.296,014

Claims.

The invention relates to a method of cementing oil and gas wells toeliminate the entrance of water therefrom as much as possible.

In actual practice it has been found that the oil occurring in the earthformations is usually floating on top of a body of salt water which actsas the motivating agent which traps the oil beneath a cap rock or otherimpervious formations in the earth. When the well penetrates a cap rockthe oil and. gas are removed. It is the object of the present inventionto close off the porous formation in the lower reaches thereof so as toshut off to the greatest extent possible the encroachment of any waterinto the well bore. When this is accomplished it has been found that theoil and gas will continue to seep into the upper reaches of theformation and enter the well so that a maximum of production can beobtained from the formation.

The present invention concerns itself with a method of cementing off thelower reaches of the formation and broadly contemplates introducing thecement in small batches at predetermined pressures at which the cementwill enter a water formation but will not necessarily enter that part ofthe formation containing oil and gas.

It is the theory of the present invention that the formation can be bestclosed off by stages, that is, that a small batch of cement isintroduced into the well bore and forced into the formation at apressure which must not exceed a predetermined amount and which iscalculated as a function of the depth of the well so as to take intoconsideration the static pressure on the formation and which is alsocalculated in a manner that the cement will not cause any scouringaction in the pores of the formation.

It is intended that a small batch of cement will be introduced so as topartially close the pores of the formation. This cement is allowed totake an initial set and then another lining or batch of cement isintroduced to further close the pores and be deposited upon the initialdeposit of cement. This building up of the cement in the pores ofchannels of the formation gradually closes the pores and thereafterprevents the migration of salt water thru the formation.

The pressures utilized to introduce the cement and the amount of cementused are of the essence of the invention because it has been found inactual practice that if too great a pressure is used the pores seem tobe clogged temporarily and thereafter the formation reopens and the jobshave been found to be unsusccessful; whereas, in other instances iflarge amounts of cement are introduced continuously it is thought thatthe cement serves to scour out the pores of the formation and beyondpredetermined limits it has been found that large quantities of cementcan be forced into the formation and the pressure required to introduceit actually falls off, rather than increasing. In some instances it hasbeen possible to pump an indefinite amount of cement into a porousformation and it entirely disappears.

Obviously all of the pores in the formation are not of the same size andnaturally the cement slurry which is introduced being rather viscouswill enter the larger pores and will only enter the smaller pores whenthe pressure at which the cement is applied is increased. It istherefore intended that batch after batch of cement will be introducedand each batch permitted to take its initial set before the next batchis introduced and these batches are small in size because only a smalldeposit of cement is to be made in each pore so that it will cause adeposit in th pore before subsequent deposits may be made.

There are various sets of conditions which are encountered in oil, gasand water wells and for purposes of illustration the following sets ofconditions are outlined: (I) Oil and water; (II) oil, water and gas;(III) gas and water; (IV) water only; (V) gas only; (VI) oil and sand;and (VII) oil and gas.

It is one of the objects of the present invention to cement an earthformation by introducing separate batches of cement to the sameformation.

Another object of the invention is to close a porous formation in theearth by introducing a batch of cement, allowing such cement to take aninitial set and subsequently introducing additional small batches ofcement so as to progressively close up the porous areas of theformation.

Another object of the invention is to introduce a small batch of cementinto a porous formation at a predetermined pressure and if theformationwill accept the cement, to then subsequentlyintroduce asecondand similar batch and to continue this procedure until the formation isgradually closed by these accumulating deposits of cement.

Another object of the invention is to introduce cement into a well at apressur in pounds per square inch not to exceed forty percent of thedepth of the well in feet plus twelve hundred pounds.

Another object of the invention is to introduce a small batch of cementslurry having a specific gravity greater than fifteen and one-halfpounds per gallon into an earth formation at a pressure calculated as afunction of the depth of the well plus a constant.

Another object of the invention is to squeeze cement into the lowerreaches of a porous formation by introducing it in small batches so asto provide accumulating deposits into pores of the formation andeventually creating a substantialas possible.

1y solid block of material which will compel any water being forced intothe formation to travel around the block of material in such a mannerthat the encroachment will necessitate depletion of the oil and gas inthe upper reaches of the formation.

Other and further objects of the invention will be readily apparent whenthe following description is considered in connection with theaccompanying drawing in which:

Fig. 1 is a side view illustrating a diagrammatic arrangement of a wellwhich is being treated in accordance with the invention.

Fig. 2 is a top plan view looking down upon an oil field in which a wellis being cemented and illustrating the manner in which the cement isforced into the porous formation.

Fig. 3 is a transverse sectional view of a pore in the formation andillustrating the accumulating deposits of cement.

Fig. 4 is a broken detail section showing the block of cement in thewater sand.

The apparatus which is utilized in practicing the invention isillustrated diagrammatically and includes a casing 2 which is positionedin the well bore and may be sealed off at its lower end by cement 3. Acasinghead 4 closes the well and has the flow lines 5 and 6 extendinglaterally therefrom. The line 5. may be controlled by a valve 1 whilethe line 6 is controlled by a valve 8.

An operating pipe ID is sealed in the casinghead and may have one branchll thereof connected to the pump 12 and another branch I3 arranged to beconnected to any suitable source of fluid under pressure or to dischargefrom the well in event the circulation is reversed.

The valve l4 in the branch I l and the valve IS in the branch I3 arearranged to control the fiow thru these lines. The section of the pumpis indicated as extending into a pit II, or it may be connected to thesuction line l8 to pump any desired type of fluid into the assembly.

Inside of the casing 2 the operating pipe I!) carries what is generallyknown as a circulating joint which can be manipulated by movement of thepipe ID to open the port 2| so as to allow flow of liquid to occureither into or out of the annular space 22 inside of the casing. Aretainer or packer 23 is arranged to be manipulated by the tubing so asto form a seal inside of the casing and may contain a back pressurevalve 24. The pipe 10 has its lower end 25 extending below the retainerso that fluid may be discharged thru the pipe into the area 26 in thewell bore below the casing 2.

The well bore is shown as having penetrated the cap rock or imperviousformation 30, the oil and gas sand 3| and the lower reaches of theporous formation at 32 which contains the water to be excluded.

The lower reaches of the formation 32 are illustrated as having largepores 40 therein, intermediate pores 4| and the smaller pores 42. Theseof course are diagrammatic and are arranged for purposes ofillustration.

What is generally known in the art as squeeze cementing is accomplishedby forcing the cement into the formation under pressure and retainingthe cement under pressure if desired until it has taken its initial setso that the blocking of the formation is insured. With the presentinvention the depth of the well is of course known to the operator andthe well is preferably cleaned out so as to have as clear a liquid inthe hole The pipe or tubing is then run into position and the cementretainer 23 properly set to seal the casing and is preferably set at anelevation just above the producing formation, such as 3| and 32. Thecasinghead 4 is arranged about the tubing 5 so as to form a seal and toclose the area 22 in the casing around the outside of the tubing [0. Thetubing H] is of course arranged to move vertically so as to operate thecirculating joint 20 and to also set or release the retainer if desired.In some instances no retainer need be used.

In a well which is filled with a column of liquid the weight of thisliquid is effective as a static pressure against the face 43 of the openformation which is exposed to such column of liquid and it iscontemplated that the cement in practicing the present invention will bepumped into the formation at a pressure which is a function of the depthof the Well. After considerable study and experimental practice aformula has been devised for ascertaining the proper pressure which isthe maximum to be used in forcing cement into a, formation. This formulahas been worked out as a pressure in pounds per square inch which iscomputed by taking such a pressure which is forty percent of the depthof the well in feet and then adding to that pressure a constant whichhas a value approximating one thousand, but which may vary, dependingupon circumstances and conditions as much as four hundred, so that itmay be considered as one thousand either plus or minus two hundred sothat the smallest maximum pressure which is to be added to forty percentof the depth of the well in feet is eight hundred and the maximum istwelve hundred.

Inasmuch as the water in the water sand 32 is usually a salt water, ithas been found that there is no coagulation or other chemical reactionin connection with the cement or the formation if a salt water is usedas distinguished from the use of a clear water which is not salty.Therefore, it may be generally understood in this description, where theterm water is used it is intended that it will be salty water which canbe detected by taste and is similar to the salty water in thatparticular well. In some instances, however, fresh water or watercontaining other chemicals may be used as circumstances require.

With the parts in the condition as above noted the well is ready to betreated and the pump 12 is operated so as to pass this salty water thruthe pipe I0 and into the area 26 in the open formation. It has beenfound that a sand such as 3| which contains oil and gas will not accepta salty water at the same pressure at which the same sand containingwater such as the lower reaches of the sand at 32. This is possibly dueto the greater viscosity of the oil in the sand and the natural pressurein the oil containing sand due to capillary attraction.

When the water is pumped into the well at the calculated pressure itwill be forced against the face of the formation 53 and will naturallytend to enter the pores 40, 4| and 32. If the water enters the poresthen the operator is aware of the fact that the well is ready to becemented. If, however, the pressure required to cause the well to acceptthe water approaches the calculated pressure, it has been found that ifsuch pressure is held on the formation for a short period of time, thatthe formation appears to crack, break down or explode in the mannersimilar toa formation which is subjected to explosives and it isprobable that this hydraulic pressure being greater than the staticpressure to which the formation was previously subjected, causes afracturing and rendering of the formation which opens up additionalareas because it has been found that after a certain critical pressurehas been reached which almost approximates the calculated pressure, thatafter this accepting effect is created, thereafter the formation willtake water at a much lesser pressure. In other instances, however, theformation will take the water readily without any fracturing orexploding consequences.

When the operator has determined that the formation will take this waterat less than the calculated pressure, he is then ready to introduce thecement.

It is believed that the introduction of large volumes of cement causes ascouring of the pores in the formation because in actual practice it hasbeen possible to introduce large volumes of cement and after a certainpreliminary amount of cement is introduced it has been found that, as amatter of fact, the pressure required to cause the formation to acceptadditional cement becomes lower and lower; whereas, one would normallyexpect the pressure to increase, due to the introduction of the cementbut this has not been found to be a fact. After making a study of thisphenomenon it was conceived that if only a small batch of cement wereintroduced and then permitted to take its initial set, that undoubtedlya thin layer or deposit of cement would occur upon the walls of thepores in the porous formation. A test could then be made to determinewhether or not the pores had been filled by introducing a batch of waterto follow the cement. It was found that a greater pressure was requiredto introduce the water following the cement than had been necessary tointroduce the cement, indicating that the pores had been partiallyclosed. After the cement had taken its initial set it was found that ifanother batch of cement was intro-- duced that another deposit was madein the pores and on the faces of the formation which still furtherrestricted the pores and after this second batch had taken its initialset, if water was introduced it was found that still a greater pressurewas required so that this procedure was repeated time and again untilthe pores were completely closed.

,As an illustration of how these deposits might be made attention isdirected to Fig. 3 where a pore 40 is shown in the formation 32.Inasmuch as this pore is in a substantially horizontal position it seemsclear that as the cement is forced into the pore it would form a depositsuch as 50 along the lower circumference of the pore, that after thisdeposit had taken its initial set the next batch would form its depositssuch as 5|, the third batch a deposit such as 52 and the fourth batch adeposit such as 53 to finally close the pore. This is merelyillustrative, however, because it is intended that a sufficient numberof batches will be introduced to close the pore. In actual practice inseveral hundred wells the maximum which has been found to be necessaryin the most porous formations has been six batches.

It is also possible that the first batch instead of making a depositsuch as 50 in the pore may close a large pore such as 40 completelybecause naturally the cement will enter the pore 40 before it wouldenter the pore 4|, due to the fact that the pore 40 is the larger sothat it is possible that the first batch might close the larger poresuch as 40, the next batch would. close pores such as 4| and thesubsequent batches would close succeedingly smaller pores. The generaltheory, however, is that the lower reaches of the porous formations suchas the water sand 32 will have the pores thereof filled with the cementso as to cause any encroachment of water to fall around the body ofwater or cement which is formed. Such a block is illustrateddiagrammatically in Fig. 4 at 55. It seems clear that any encroachmentof water to get into the sand 3| would have to pass around the block 55and could only move into the sand 3| upon depletion of the oil and gastherein so that it has been found that in actual practice, cementing ofthe well by this batch method results in a substantial reduction if notelimination of the water and a very substantial increase in theproduction of oil or gas.

There is another phase of the theory of operation which is illustratedin Fig. 2 where the outline 50 illustrates an oil field and a particularwell such as the well of Fig. 1 is shown at 6|. The water encroachmentin a well near the edge of the field would come from the outer edge ofthe field. Naturally therefore the sand 32 toward the outer edge of thefield or the lower right hand side of the well 3| as defined in Fig, 2would be the most porous and it is quite likely that when the firstbatch of cement is introduced that it would flow along the line of theleast resistance and it would possibly take the configurationillustrated by the outline 62. The next batch of cement following thefirst would follow the path of the next least resistance and might takethe configuration of the outline 63 or it might split up and follow theoutline 64 as well as the outline 63. The next succeeding batches mightfill out the periphery around the well bore such as the batches 65 and66. This is believed to occur because of the fact that the pressurerequired to introduce the succeeding batches of cement graduallyincreases, indicating that either the sand is less porous and requiresmore pressure; the area which will accept the cement is lesser or thecement is being forced thru a greater amount of sand in order to beintroduced.

With the well 6| as viewed in Fig. 2 after all of the batches of cementhave been introduced it seems clear that a solid block such as 55 hasbeen formed which will practically prevent the encroachment of water.

As will be apparent from the seven types of Wells which are to betreated, the different wells must be treated differently and in someinstances the pressure in pounds per square inch is computed at 40% ofthe depth of the well plus one thousand or the maximum pressure which ithas been found advisable to use is two hundred greater than the onethousand, while in other instances the one thousand less two hundred canbe used as the maximum so that the constant to be used will have amaximum value of twelve hundred and a minimum value of eight hundred, itbeing desirable to exceed the minimum of eight hundred only when thecalculated pressure using eight hundred is found to be insufficient tocause the cement or the water to be admitted to the formation.

The cement undoubtedly enters cracks, crevices, channels, fissures,large pores, quick sand or a porous zone having a high permeability andit has been found that if this cement cannot be squeezed into theformation at the calculated pressure of forty percent of the depth plusa maximum constant of twelve hundred, that the formation is probablyfilled and additional pressure is unnecessary and probably dangerousbecause the pressure above that calculated might force the cement intothe production zone of the oil or the gas and destroy the well.

In practically every instance where a batch of cement is introduced itis desirable to follow it by enough water to displace the cement fromthe area 26 in the well bore beneath the retainer 23 and of course thevolume of this area plus the volume of the pipe can be determined sothat a definite amount of water can be added which acts as a. plug toforce the cement along ahead of it and it has been found in actualpractice that if this theory is followed that after the cementing hasbeen completed and the well is cleaned out, that in many instances thewell bore has been practically free of cement.

In some instances where all of the cement cannot be forced into theformation by the addition of this slug of water without exceeding thecalculated pressures, cement may be left in the tubing 10 and to removethis before it sets the circulation from the pump l2 can be reversed byclosing the valve l4 and opening the valves 8 and I5. The tubing then ismanipulated to open the circulation joint and allow water to flowdownwardly into the area 22 into the port 2! and should wash out thetubing ID by discharging the water thru the branch l3.

The initial set of the cement has been found to require about threehours but of course this period may vary depending upon the temperatureand pressures encountered and it has been found With wells of less thanfour thousand feet that cement on the market known as Portland OilwellCement is preferable because of its setting propertles but with wells ofa greater depth than four thousand feet ordinary cements which areresistant to high temperatures can be used satisfactorily.

In some instances a single small batch may be sufficient to shut off orreduce the undesirable fluid, be it gas or water, because the smallbatch does not scour out the pores of the formation.

In some wells having a low fluid level sufficient pressure might notobtain from the first batch of cement and care is necessary to avoidscouring out the first batch so that if the pressure does not build upto anywhere near the calculated pressure when introducing the firstbatch of cement, then this batch should be followed by as little wateras possible, merely enough to displace the cement into the formation andout of the tubing I0 and the area 26 in the well below the retainer. Inorder to check these calculations it may be necessary to run wirelinemeasuring devices into the well so as to be sure that all of the cementhas been displaced.

The size of the batch of cement is of vital importance and in actualpractice it has been found that a batch of more than fifty sacksevidently causes scouring in the porous formation because the pressuredrops off after the introduction of approximately fifty sacks and themaximum pressure is obtained when introducing about thirtyfive sacks andfor this reason thirty-five sacks has been determined as the mostadvantageous amount to be introduced in any one batch. Of course thismay vary depending upon the depth of the hole 26 or the depth of theformation 32 into which it is being introduced and in some instances thediameter of the hole, while the nature of the formation will also havean important bearing upon the exact technique to be followed in anyparticular well.

Cement will not set in a gas zone unless the formation has first beenkilled by inpumping water.

It has been found that it is impossible to cement both a water and a gassand at the same time with a single batch of cement because if eithersand accepts the cement it will not penetrate the other sand but wherethe present batch method is followed a batch is forced into one sand andthe next batch into the other. Thus the lower area 32 of Fig. 1 could becemented with one batch and the gas at the top of the portion 3|cemented with another batch.

In some instances if the area 26 is of considerable length the lowerreaches of the formation may be closed by desisting from the pumpingoperation before all of the cement is discharged from the area 26 andafter the upper portion of the formation has been treated, then thisblock can be cleaned out of the lower portion and the lower reaches ofthe formation then subjected to the batch treatment.

The present invention is useful in determining at what elevation or intowhat formation the water leaves or enters the well. Thus if it is knownthat say thirty barrels is the volume of the pipe l0 and area 26 andwhen water is pumped in behind the cement it is found that the pressuredrops off, when say twenty five barrels have been introduced, it then isprobable that five barrels of cement remain in the bottom of the holeand that the water has broken thru the formation at a point just abovethe cement. On the other hand if all the thirty barrels enters the wellwithout any drop in pressure it is an indication that the cement is alldisplaced.

It has been found that after a batch has been completed it is best toallow a permanent set to occur for a period of three days and whendrilling out the batch it is best to discontinue drilling when two orthree feet from the bottom of the bore 26 and to watch carefully thenature of the cement bein drilled and in any event to stop drilling whenthe bit passes from soft cement into hard cement.

There are certain essential instructions or conditions which must befollowed in the various types of wells being cemented and for purposesof illustration the following rules are given which should be followedin practicing the invention:

I. Pressure to be applied is figured at 400 pounds per thousand feet ofhole plus 1,000 pounds (constant), plus or minus 200 pounds, i. e. a4,000 foot well requires a minimum pressure of 2400 pounds per squareinch and a maximum pressure of 2800 pounds (4,000 x .40, plus 1,000 plusor minus 200) This pressure should always be corrected for any fluid butwater in the tubing, and the surface pressure therefore assumes a columnof water in the tubing to the bottom of the well.

A. Insufficient pressure may not effectively shut off the water in awell bore open to production and the minimum pressure must be attained.

1. It is desirable that the squeeze operations result in pipe line oilwells (no water), for if this is not attained, the well will usuallyreturn to its previous condition within thirty to ninety days.

(a) This does not apply to the water which at first appears with theoil, and decreases day by day until water is no longer present in theoil. This seldom exceeds ten percent and should fall to three percent ina week.

(b) A shallow well usually must be bailed dry before the oil willreenter the bore of the hole after squeezing.

B. Excess pressure not only shuts off the water but frequenly delays thereentry of oil into the bore of the hole after the squeeze operation,and in some formations shuts off the oil as well as the water entirelybecause the oil formation may be fractured.

1. Fresh water pumped into the oil zone sometimes delays the reentry ofoil and for this reason it is advisable to use formation water which isnot too salty and whose S20 content is dissipated.

(a) When squeezing wells that contain bentonite mixed with the oil sand,it is almost imperative that salt water be used even to mix the cement,to prevent excessive swelling.

II. Small batches of thirty to forty-five sacks of cement are to be usedat a time, squeezed into the bore of the hole and displaced into theformation where it is allowed to set for about three hours.

A. The type of cement used is governed by the depth of the well.

1. Always mix the cement 15.5 pounds per gallon or heavier.

(a) A thin mix even though placed and set, is not strong enough towithstand production pressures.

(b) The heaviest mix is considerably diluted when it enters waterbearing channels.

2. Use Portland oil well cement in wells less than 4,000 feet deep andwells whose temperatures are less than 125 in the formation.

(a) Be sure to specify oil well cement, as builders cement usually doesnot set effectively in the neat mix.

(1)) This cement should take an initial set in from not less than oneand. one-half hours to not more than two and one-half hours at thesurface.

Too fast a set will set in oil bearing channels before the oil has timeto penetrate the slurry and prevent the set.

Too slow a set will permit the water to dilute or disturb the cement tosuch an extent it will not set effectively if it is still in position.

3. Use slow set cements in deep high-temperature wells.

4. Do not use adulterants in the cement mix because the strength isreduced and uneven hydration may result.

(a) Bentonite only weakens the strength of the cementthe angle ofrepose, for which purpose bentonite is usually used, is higher with aheavier cement than would be possible by the addition of the adulterant,and still be pumpable. Such adulterants also increase the coefficient ofexpansion, causing the set cement to shrink from the wall of the channelafter setting.

5. Test every batch of cement pumped into the well, by taking a sampleof the actual mechanically mixed slurry that is being pumped therein, asthis is the only accurate check yet known for successful operations.

B. The ultimate success of the operation restricts the size of thebatches to thirty to fortyfive sacks each.

1. Less than thirty sacks does not always produce a higher subsequentpumping pressure, therefore is not always effective.

2. More than forty-five sacks causes the loss of pressures alreadyraised, because it is so abrasive and only cuts a larger channel in theformation instead of partially filling it.

3. If the cement job has failed behind the casing, the first small batchwill go there and by being allowed to set, will prevent subsequentpressures during operation from going up behind the casing, collapsingit on the tubing.

4. If the maximum predetermined cementing pressure is arrived at, beforeall of the thirty-five sacks have been pumped into the formation, itrequires very little pressure on the casing of the 'Well to reverse theexcess out of the tubing.

(41) Tubing full of cement in a 4,000 foot well will require nearly2,000 pounds pressure to reverse out of tubing, and this pressure mayeasily rupture the casing. Such an operation is further endangered bythe possible break-down of mechanical equipment.

(1)) No well has yet required more than six batches of thirty-five sackseach properly applied to obtain the required pressure, and this has solowered the cost of the cement used, that the retainer pays for itselfas much as ten times over.

C. Follow each batch of cement with enough water to clear the bore ofthe hole below the cement retainer, to the bottom of the well.

1. Cement slurry will enter the largest channel and the following waterwill enter the smaller unfilled channels, if the cement enters formationabove the bottom of the hole.

(a) This leaves the bore of the hole clear for subsequent operations.

2. Cement will not enter formation appreciably unless there are cracks,crevices, pores or quicksands present.

(a) Water cannot be pumped thru an oil saturated sand with a porosity asgreat as 500 millidarcys, even at extreme pressures.

(b) It is also difficult to pump oil thru a water saturated sand undersimilar conditions. This is most attributable to the emulsification andincreased viscosity of oil and water.

3. While pumping a batch of cement into the hole, if the pressure risesto the maximum predetermined pressure, and stands for five minutes,cease operations.

4. If the testing water pressure after waiting three hours after a batchof cement has been pumped into the bore of the hole, stands for tenminutes at the minimum pressure, predetermined, cease operations.

(a) Even though there is no cement left in the bore of the hole, ifwater cannot be pumped therein at these pressures, the well will notproduce water, unless there is some bridge or other undeterminedobstruction in the hole.

5. The well should not make water as long as new original (virgin) holeis not made.

(a) As a protection when drilling in, it is sometimes advisable to makeextra hole in shallow horizons before squeezing to allow for thiscontingency.

III. Allow at least thirty-six hours before drill. ing out the retainerand three days before testing the hole,

A. Stop drilling operations when the cement changes from soft to hard,after drilling below the bottom of the casing, and try for production.

1. It is desirable that the well be bailed or swabbed, or pumpedthat allfluid be removed from the hole, for a complete test to allow the waterto find new channels to flood the oil into the bore of the hole.

(a) A squeezed well can seldom if ever be jetted in because of thepressure of the gas on the producing zone.

B. If the cement is hard all the way down the bore of the hole, stopdrilling a few feet from the original bottom and test. (I. A. 1)

C. Allow the well at least three days for the oil to reenter.

1. After the oil starts into the bore of the hole, full potential, ifthe well is produced intensively, will occur in a week or ten days, oras soon as the water pumped into th formation during squeeze operationshas been recovered.

IV. Never acidize after a squeeze operation ex cept as a last resort.

A. If acidizing is necessary, it should be done before squeezing and mayeven be done thru the retainer before or during batch squeezing as thismay be the only means to force acid into oil bearing horizons due toacids greater affinity for water bearing limes.

B. All new Wells that must be acidized for production should be squeezedthereafter to shut off the water that enters because of acid about 95%of the time.

V; The recovery of oil after shutting off Water may be normally expectedto increase three to five times on wells making less than 20 barrels perday, with all the water the pump can handle, thereafter making no waterand requiring pumping only a few hours daily, with a minimum of rod,tubing, pump and unit break-downs.

A. This refers to steady production only, and excludes large initialproducers whos production is usually erratic.

B. The water may be excluded in large producing wells at least withoutreduction of potential production.

VI. This entire method is not operable to my knowledge for the reductionof gas in waterwhite distillate producers, nor for the exclusion ofwater in wells which produce fresh water without minerals of any kind inappreciable quantities (affect normal taste).

VII. This method is operable to the same degree, whether reducinggas-oil ratios, or excluding water at any depth, or both with onesetting of a cement retainer.

A. The single operable exception to this method (excluding VI) is theexclusion of water in a gas well.

1. Instead of squeezing batches until the predetermined pressure isreached, the operations are halted when there is a subsequent drop inpressure after a previous batch of cement has been placed.

(a) This drop indicates that the water is entering the gas zone, insteadof a water bearing channel.

B. The success of this method has been conclusively demonstrated inwells from 900 feet deep to 12,000 feet after previous diligentlyapplied methods have failed-with or without the assistance of a cementretainer, and includes all generally known types of formation.*

C. It has been also conclusively demonstrated that it is impossible toshut off both water and gas with any single batch of cement when equallyexposed under normal well conditions.

While the shutting off or reducing of water has been specificallydescribed it is intended that the shutting off or reducing of any fluidsuch as a gaseous fluid is intended.

*I herein refer to unconsolidated sands, thin lenses containing both oiland water, all lime formations, as well as their interlying dobies orclays, with the exception of serpentine which I have not attemptedbecause of the nature of this production make a squeeze appearfoolllardy.

Conclusion The squeeze operation essentially places a large block ofcement somewhere into the formation and so increases the area around itthru which the water must channel, that it merely exerts a pressure onthe bottom of the oil flooding it into the bore of the well and does notgain sufiicient velocity to cut a channel around the plug.

What is claimed is:

1. A method of cementing a porous formation in a well to shut off theencroachment of an undesirable fluid which comprises introducing a smallbatch of cement slurry into the formation, permitting an initial'setthereof, introducing a second batch, allowing an initial set thereof,and testing theformation.byarzplxi a liquid pressure oflss 'than apredetermined amount which is computed as a proportion of the depth ofthe well being cemented, plus a constant which may vary between eighthundred and twelve hundred.

2. A method of cementing a porous formation in a well to shut oif theencroachment of an undesirable fluid which comprises introducing a smallbatch of cement slurry into the formation, permitting an initial setthereof, introducing a second batch, allowing an initial set thereof,testing the formation by applying a liquid pressure of less than apredetermined amount which is computed as a proportion of the depth ofthe well being cemented, plus a constant between eight hundred andtwelve hundred, and repeating such batch procedure and alternate testingwith liquid pressure until the pressure required to force liquid intothe formation approaches the calculated pressure.

3. A method of introducing cement in batches into a well bore to closeoff a porous formation which comprises the steps of forcing a batch ofcement slurry into the formation at a pressure in pounds per square inchwhich does not exceed an amount calculated as forty percent of the depthof the well in feet plus a constant of twelve hundred.

4. A method of introducing cement in batches into a well bore to close01f a porous formation which comprises the steps of forcing a batch ofcement slurry into the formation at a pressure in pounds per square inchwhich does not exceed an amount calculated as forty percent of the depthof the well in feet plus a constant of twelve hundred, allowing thecement to take an initial set, and testing to see if the formation isstill porous by applying a liquid to the formation at a pressure whichdoes not exceed the calculated pressure.

5. A method of introducing cement in batches into a well bore to close01f a porous formation which comprises the steps of forcing a batch ofcement slurry into the formation at a pressure in pounds per square inchwhich does not exceed an amount calculated at forty percent of the depthof the well in feet plus a constant of twelve hundred, allowing thecement to take an initial set, testing to see if the formation is stillporous by applying a liquid to the formation at a pressure which doesnot exceed the calculated pressure, and repeating the cementing andtesting until the calculated pressure is approached while introducingeither the cement or the liquid.

6. A method of introducing cement in batches into a well bore to closeoff a porous formation which comprises the steps of forcing a batch ofCement slurry into the formation at a pressure in pounds per square inchwhich does not exceed an amount calculated as forty percent of the depthof the well in feet plus a constant of twelve hundred where the batchdoes not exceed forty-five sacks of cement mixed into a slurry.

7. A method of introducing cement in batches into a well bore to closeoff a porous formation which comprises the steps of forcing a batch ofcement slurry into the formation at a pressure in pounds per square inchwhich does not exceed an amount calculated as forty percent of the depthof the well in feet plus a constant of twelve hundred where the volumeof liquid does not exceed that required to empty the well bore ofcement.

8. A method of introducing cement in batches into a wellbore'to closeoff a porous formation which comprises the steps of forcing a batch ofcement slurry into the formation at a pressure in pounds per square inchwhich does not exceed an amount calculated as forty percent of the depthof the well in feet plus a constant of twelve hundred where the batchdoes not exceed forty-five sacks of cement mixed into a slurry, andwhere the volume of liquid does not-exceed that required to empty thewell bore of cement.

9. A method of closing porous formations about a well bore whichcomprises introducing a batch of cement slurry to form a depositpartially filling the pores of the formation, allowing the depositedslurry to take an initial set, subsequently making additional depositsuntil the pores are filled, and. testing for porosity by applying liquidpressure after each batch where the pressure in pounds per square inchdoes not exceed an amount calculated as forty percent of the depth ofthe well in feet plus twelve hundred.

10. A method of cementing wells to shut off the entrance of water whichcomprises the steps of pumping salty water into the well at a pressurein pounds per square inch which does not exceed the amount calculated asforty percent of the depth of the well in feet plus twelve hundred, thenintroducing into the well a batch of not more than forty-five sacks ofPortland 011 well cement mixed with water to form a slurry having aspecific gravity of not less than fifteen and one-half pounds pergallon, following the batch with salty water until the batch of cementis displaced from the well bore into the formation at a pressure notexceeding the calculated pressure, allowing the cement to take aninitial set, then introducing alternately additional salty water andsimilar batches of slurry into the formation and allowing the cement totake an initial set before introducing the salty water, and repeatingthe procedure until the pressure required to introduce the cement or thewater reaches the calculated pressure.

RAY S. KAIL.

caret teem

